1. Field of Invention
This application is Application directed to a high speed data cable configured to improve alien crosstalk isolation between adjacent cables and/or improved crosstalk between twisted pairs of a cable.
2. Discussion of Related Art
High-speed data communications media include pairs of wire twisted together to form a balanced transmission line. Such pairs of wire are referred to as twisted pairs. One common type of conventional cable for high-speed data communications includes multiple twisted pairs that may be bundled and twisted (cabled) together to form the cable. There are two general categories of twisted pair cables: unshielded twisted pair (UTP) cables and shielded twisted pair (STP) cables, each of which has advantages and disadvantages. For some applications, the preferable cabling structure is “unshielded twisted pair” (UTP) cabling, meaning that the individual twisted pairs making up the cable do not have individual shielding layers. UTP is often preferred over shielded cables (and over optical fiber cables) because it is easier to install and more cost-effective.
Modern communication cables must meet electrical performance characteristics required for transmission at high frequencies. The Telecommunications Industry Association and the Electronics Industry Association (TIA/EIA) have developed standards which specify specific categories of performance for cable impedance, attenuation, skew and crosstalk isolation. When twisted pairs are closely placed, such as in a cable, electrical energy may be transferred from one pair of a cable to another. Such energy transferred between pairs is referred to as crosstalk and is generally undesirable. When two or more cables are stacked close together, or bundled together in a common outer sheath, an additional problem of crosstalk between twisted pairs in adjacent cables can occur. This is known as “alien” crosstalk. The TIA/EIA has defined standards for crosstalk, including TIA/EIA-568A. The International Electrotechnical Commission (IEC) has also defined standards for data communication cable crosstalk, including ISO/IEC 11801. One high-performance standard for 100Ω cable is ISO/IEC 11801, Category 5e, another is ISO/IEC 11801 Category 6.
Ethernet is now the most widely used network protocol in the world and there is an ever-increasing need in the industry for cables capable of reliable Ethernet data transmission at higher and higher transmission rates. A few years ago, transmission rates of a few Megabits per second (Mbps) were considered the state of art. However, transmission rates of more than ten Gigabits per second (Gbps) are now expected. The higher the desired transmission rate of data through a cable, the more critical becomes controlling effects such as crosstalk, skew and attenuation. Accordingly, a new 10 Gbps Ethernet over UTP standard for enhanced category 6 cables is being developed. One critical factor that needs to be addressed in the design of enhanced category 6 cables cable of 10 Gbps transmission rates is alien crosstalk. Alien cross-talk coupling, from the outside of the cable into the twisted pairs, is statistical and cannot be compensated for by adaptive amplifier techniques. Therefore, it is important to address alien crosstalk in the design of the cable itself.
To further reduce crosstalk between twisted pairs within a cable, some cables include a pair separator disposed between the twisted pairs to shield and/or isolate the twisted pairs from one another. For example, U.S. Pat. No. 6,222,130 describes a cable that includes four twisted pair media radially disposed about a “star”-shaped core. Each twisted pair nests between two fins of the “star”-shaped core, being separated from adjacent twisted pairs by the core. This helps reduce and stabilize crosstalk between the twisted pair media.
Some effort has been made in the prior art to reduce the effect of alien cross-talk on signal pairs in data cables. For example, some data communication cables include outer jackets having irregular or asymmetrical structures, as shown in FIG. 1. FIG. 1 depicts a communication cable including a plurality of twisted pairs 102 of insulated conductors surrounded by a cable jacket 100. The “dog-bone shaped” configuration of the cable jacket 100 shown in FIG. 1 increases the center-to-center distance between identical twisted pairs similarly positioned in the neighboring cables when stacked in alignment. The shaped outer jacket 100 may also achieve a misalignment by shape-induced sideways shifting of one cable relative to another, thereby preventing the possibility of positioning twisted pairs of the same twist lay very close together.
The shape of cable jacket 100 prevents symmetric stacking of flat data communication cables, when such cables are installed in ducts, troughs, and locations close to the cross-connect panels. Otherwise, the flat cables may automatically arrange, align and stack themselves in near perfect alignment due to their flat or rectangular shape. Such arrangement or flat cables increases alien cross-talk because the location of the twisted pairs within a flat cable jacket is parallel and the twisted pairs with the same twist lays or directions would be frequently separated only by the jacket material surrounding each cable.
However, a drawback to the shaped-jacket method of controlling alien crosstalk is that it is not always convenient or desirable to manufacture cables with irregularly-shaped outer jackets such as the cable jacket shown in FIG. 1. Therefore, a need exists for a mechanism to reduce alien crosstalk between adjacent cables that may have similar or identical twist lay configurations, while retaining a fairly conventional, easy to manufacture, outer jacket shape. Ideally, this mechanism would be appropriate for UTP cabling.